The production of mouse cochlear and organ of Corti cDNA libraries is under way. These libraries will be used to genetically define and study hereditary hearing disorders and are also expected to serve as a valuable resource for the study of the physiology of the organ of hearing. Last year, tissues from the mouse were collected for the production of three different cDNA libraries; all tissues were from young, adult mice. One library will be based on RNA from the whole cochlea; another represents the apical half turn of the organ of Corti together with a thin strip of tissue on which this piece of the organ of Corti is resting; and the third will be made from the basal turn of the cochlea, i. e. of the organ of Corti together with the vascular stria and the spiral ligament from this region.